This is a proposal for a collaborative research project between Dr. Angel Caputi of the Instituto de Investigaciones Biologicas Clemente Estable in Montevideo Uruguay and Dr. Curtis Bell of the Neurological Sciences Institute at Oregon Health Sciences University in Portland Oregon. Dr. Bell's grant, MH49792, is the Parent Grant for this project. This project is concerned with the central nervous system of electric fish of the order Gymnotiformes, an order of fish which is native to Uruguay and other parts of South America. More specifically, this project is concerned with gymnotiforrn fish in which the electric organ discharge is a brief pulse of electric current. The goals are to establish the functional circuitry of the electrosensory lobe (ELL) of these fish and to compare it with that of the ELL of pulse electric fish of the order Mormyriformes, an order of fish that is native to Africa and which is being studied in the laboratory of the Principal Investigator, Dr. Bell. The ELLs of both groups of fish are cerebellum-like structures where sensory information from the periphery is first analyzed by the brain. The ELLS of pulse mormyriform fish and the cerebellum-like structures of some other groups of fish have been shown to act as adaptive sensory processors in which predictable features of the sensory inflow are subtracted from current sensory inflow through memory-like processes - allowing novel, information-rich sensory information to stand out more clearly. Plasticity at the synapse between parallel fibers and Purkinje- like cells has been demonstrated in some of these fish, and is the probable mechanism of the memory-like processes. The hypothesis has been advanced that all cerebellum-like sensory structures in vertebrates, including the ELL of pulse gymnotiforms and the dorsal cochlear nucleus of mammals, are functionally similar and act as adaptive sensory processors. Little is known at present concerning the ELL of gymnotiform pulse fish, a major group of electric fish. This project . will determine the circuitry and test for synaptic plasticity in the ELL of these fish using intracellular recording in the in vitro slice preparation. The results will permit a significantly richer comparison of the different cerebellum-like structures and a deeper knowledge of how they analyze and store sensory information.